The present invention relates to accessory units for use with citizens band (CB) radio transceivers operating in the 27 Mhz frequency band. With the increased interest in CB radio, CB equipment users and operators have become more sophisticated and many demand optimum performance from their equipment. It is well known in the radio art to employ various test and measuring sets such as standing wave ratio (SWR) monitoring circuits for monitoring transission lines, radio frequency (RF) power detection circuits for measuring power, and field strength detection circuits to determine the quality of performance of radio equipment. While the foregoing types of RF measurements can be made with CB radio equipment, it is then also necessary to use impedance matching networks to match the transceiver-transmission line to the particular antenna system if the RF system performance is to be optimized. It is also desirable for an accessory unit to provide simple means for connecting various antennas or combination of antennas to a CB radio transceiver and to provide dummy load means to facilitate tune up and/or testing of the RF signal modulation. Prior art CB radio accessory units have not combined these various features into a single, simple-to-operate unit.